Apparatus for coating tubular fluorescent lamps



APPARATUS FOR COATING TUBULAR FLUORESCENT LAMPS 3 Sheets-Sheet 1 Filed May 1, 1952 FigZ.

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APPARATUS FOR COATING TUBULAR FLUORESCENT LAMPS 3 Sheets-Sheet 2 Filed May 1, 1952 lnven tovs: Evnes l: G.Bowbes, Edward BMILES, by p/w Theiv A t ovneg.

June 12, 1956 E, s. BOWLES ET AL 2,749,847

APPARATUS FOR COATING TUBULAR FLUORESCENT LAMPS Filed May 1, 1952 5 Sheets-Sheet 3 Invervtovs: Evns l: G. Bowtes, Edward E.MiLes,

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United States Patent APPARATUS FOR COATING TUBULAR FLUORESCENT LAMPS Ernest George Bowles, London, and Edward Ernest Miles, Wernbley, England, assignors to General Electric Com= puny, a corporation of New York Application May 1, 1952, Serial No. 285,4il6 Claims priority, application Great Britain May 3, 1951 1 Claim. (Cl. 103-236) This invention relates to apparatus for coating the interior of tubular electric discharge lamp envelopes with fluorescent material, of the kind in which the material, in the form of a powder suspended in a suitable liquid, is arranged to be introduced into the top end of a tubular envelope held either inclined or vertical, and the suspension (flowed to flow over the interior of the tube under gravity.

In use of the apparatus the excess suspension is allowed to drain out of the lower end of the tube and the tube is then passed to a drying stage to evaporate the liquid and leave a deposit of the fluorescent material on the interior wall.

Such apparatus usually includes a tank arranged to lie beneath the lower end of the tube for receiving the excess suspension and a pump for pumping the suspension from the tank to an upper reservoir from which it can flow to the top of the tube.

in such apparatus we have found that pumps of the kind used hitherto are liable to introduce foreign matter into the suspension, especially by the wear of high speed moving parts, which foreign matter may be detrimental to the quality of the coatings formed by the apparatus, and the object of the invention is to provide apparatus less subject to this difficulty.

According to the invention apparatus of the kind re ferred to comprises, in combination, a reservoir tank containing a suspension of the fluorescent powder in a suitable liquid and situated below the level of the lower end of the tube to be coated, a pipe system including a vacuum operated pump assembly arranged to pump suspension frcm the reservoir tank to a feed reservoir situated at a higher level than the top of the tube, an outlet pipe from the feed reservoir leading to the top of the tube to be coated and controllable valve means for feeding a determinate quantity of the suspension from the outlet pipe into the top of the tube to be coated.

Preferably the vacuum pump assembly is of the difiierential lioat type, that is to say, of the type wherein two floats are arranged to be raised within a pump body by liquid drawn into the pump body through an inlet valve by an applied vacuum, one being a low level float which is arranged to abut against a vacuum release valve when the liquid is at a lower level within the pump body and to be prevented from further rise by said abutment without opening the valve, and the other being a high level float which is arranged to rise with the continued intake of liquid so as to abut against the vacuum release valve or the low level float when the liquid has risen to' a higher level, the valve being arranged so as then to open and release the vacuum under the combined buoyancy of the two floats and cause liquid to be discharged from the pump body through an outlet valve, the low level ice float holding the vacuum release valve open during discharge of the liquid until the liquid has reached the lower level at which the lower level float begins to fall.

One such differential float type pump will hereinafter be described in detail with reference to its use in a particular embodiment of the invention.

Preferably the apparatus includes a constant head feed reservoir situated above the tube to be coated and into which the suspension is arranged to be fed from the pump, the outlet from this-reservoir being arranged to feed a valve nozzle assembly which can be inserted into the top end of the tube, and which is provided with means to control the flow of the suspension into the tube, so that the flow can be turned on or off at will. The amount of suspension applied to the tube can then be regulated by the length of time it is allowed to how, and this enables coatings of uniform thickness to be readily obtained. The control means may be adapted for automatic or manual control as required.

If the apparatus is arranged for coating a tube in a position other than with the tube axis vertical, it should also include means for rotating the tube about its axis in order to enable uniform coatings to be obtained.

In apparatus in accordance with the invention for coating the interior of a vertical held tube, the suspension should, of course, be introduced all round the inner wall so as to flow over the whole of the interior of the tube. Preferably this is effected by the use of a valve nozzle assembly comprising a hollow cylinder closed at its lower end and provided with a plurality of holes pierced through the curved wall near the closed end and spaced symmetrically round the axis of the cylinder. This cylinder, which may be called the nozzle cylinder, is attached in the vertical position, with its closed end downwards, to the supply pipe from the constant head feed reservoir and is arranged to be placed inside the top of the vertically held lamp envelope which is to be coated.

A suitable means for controlling the flow of suspension from the nozzle cylinder comprises an additional cylinder arranged to be a close fit around the nozzle cylinder free to rotate relatively to the nozzle cylinder, and provided with a plurality of holes corresponding to the holes therein, the holes in the two cylinders being arranged to align with each other in one position of the outer cylinder relative to the nozzle cylinder, rotation of the outer cylinder about the inner cylinder thus blocking and unblocking the holes in the nozzle cylinder and so controlling the flow of suspension.

A suitable suspension for use in apparatus in accordance with the invention may comprise, for example, 1 kg. of fluorescent powder with every 1200 ccs. of nitro-cellulose solution having a viscosity of approximately 50 centipoises. The various parts of the assembly should, of course, be constructed of stainless steel or other suitable material which will not react with the suspension.

The invention will now be further explained by describing, by way of example with reference to' Figures 1 to 5 of the acompanying drawings, two embodiments of it arranged for automatically coating the interior of electric discharge lamp envelopes whilst they are held respectively with their axes vertical, and with their axes inclined at an angle to the vertical.

Figure 1 shows schematically the relative positions of the various parts of the apparatus,

Figure 2 shows a particular valve nozzle assembly, for coating tubes in the vertical position, and

Figure 3 represents a transverse cross section of a vacuum operated pump of the differential float type.

Figure 4 shows part of a suitable conveyer arrangement for feeding tubes, arranged to be coated whilst held with their axes vertical, to and from the coating position, and

Figure 5 shows an arrangement according to the invention adapted for coating tubes whilst they are held in a sloping position.

Referring now to Figure l, the apparatus for coating vertically held lamp envelopes comprises a reservoir tank 1 connected by means of a pipe 2, to a vacuum operated pump 3 situated above the tank, the outlet of the pump being fed to a constant head feed reservoir 4, the overflow pipe 6 of the reservoir 4 leading back to the tank 1. The outlet pipe 7 from the constant head feed reservoir 4 leads to a valve nozzle assembly 8 for feeding the suspension into the top end of a tube 22 shown held in the coating position. A gauze filter 5 situated at the bottom of the pipe 2 ensures that the suspension is filtered before being drawn into the pump.

Referring now to Figure 2 the valve nozzle assembly 8 comprises two stainless steel cylinders 9, 10. Cylinder 10 is arranged to fit closely round cylinder 9, and each cylinder has both an open and a closed end. The inner or nozzle cylinder 9, which is arranged with its closed end downwards, has a stainless steel pipe 11 screwed into its open end, the other end of this pipe being connected to a length of flexible stainless steel tubing 12, which is, in turn, connected at the other end to the outlet pipe 7 of the constant head feed reservoir (not shown).

The nozzle cylinder 9 is provided with eight holes 13, each having a diameter of inch, pierced through the curved wall near the closed end, four of the holes being situated around the circumference at 90 intervals in a plane normal to the axis of the cylinder, and the other four holes being arranged also at 90 intervals in another plane normal to the axis. The two planes are separated by /2 inch, and the said other four holes are offset by 45 with respect to the first four holes.

The outer cylinder 10 is fitted closely around the nozzle cylinder 9 also with its closed end downwards and provided with two sets of four holes 14 corresponding to the holes 13 in the nozzle cylinder 9. The outer cylinder 1!) is arranged to rotate with respect to the nozzle cylinder 9 so that the holes 13 in the nozzle cylinder may be blocked or unblocked, thus controlling, in operation of the assembly, the flow of suspension. The outer or control cylinder 10 is kept in place by a screw 15 which passes through a horizontal slot 16 cut in the wall of the cylinder, and is screwed into a threaded hole in the nozzle cylinder 9, the length and width of the slot being such that the control cylinder can be rotated for about 45 with respect to the nozzle cylinder, but is not allowed to move in an axial direction. The control of the outer cylinder 10 is achieved by movement of a short arm 17 which is rigidly attached to the cylinder. The operation of the arm 17 is arranged to be automatically effected by means operated by the movement controlling mechanism (not shown) of the conveyer carrying the tubes and is arranged to open the nozzle after the nozzle has been inserted into the top of a tube and to close it before the nozzle is removed.

Around the pipe 11 connected to the nozzle cylinder and rigidly attached to it is fitted a metal strip 19 bent in the form of a cylinder and provided with a flange 20, to this flange being. rigidly attached one end of a movable arm 21 which is pivoted at the other end so that it can move only in a vertical plane as indicated by the arrow. Thus the valve nozzle assembly may be raised and lowered radially for inserting the end of the nozzle into and withdrawing it from the top of a lamp envelope 22, the short length of flexible tubing 12 between the constant head feed reservoir outlet pipe 7 and the valve nozzle assembly 8 allowing this movement to be made.

The vacuum-operated pump which is shown in detail in Figure 3, and which represents an axial section, is of the differential float type, and comprises a substantially cylindrical body 23 the top end of which is closed except for a pipe 24 through which the vacuum can be applied, and an air inlet valve 25 which is normally in the closed position.

The inlet 26 for the pump is at the side of the body near the lower end and is connected to an inlet valve 27 and an outlet valve 28 for the suspension, the inlet pipe 2 to the pump being connected to the reservoir tank and the outlet pipe 2' to the constant head feed reservoir.

In the body of the pump is a compound float comprising two separate floats 29, 30, one 29 being in the form of a hollow-walled hollow cylinder, arranged with its axis vertical, and coincident with that of the pump body, and the other 30, which will hereinafter be referred to as the air valve operating float, consisting of a float body 31 with a stem 32 attached to it. The stem 32 is arranged to lie along the axis of the cylindrical float and free to move within it, the float body 31 of the air valve operating float 30 being beneath the cylindrical float 29 and the top of the stem 32 protruding beyond the top of the cylindrical float. At the top of the stem 32 and coaxial with it is attached a cylindrical disc 33, and a spring 34 is attached to the lower end of the float body 31 to prevent the float body hitting the bottom of the pump cylinder 23; a similar spring 35 above the float body 31 prevents the two parts of the float from contacting each other.

The action of the pump is such that when a vacuum is applied through the tube 24 at the top of the pump the suspension is drawn into the body of the pump through the inlet valve 27 which is lifted from its seating, the outlet valve 28 being held closed. As the suspension rises in the pump the air valve operating float 30 is the first float to rise lifting the cylindrical float 29 with it and the top of the former abuts against the air valve 25, although, since the valve is weighted, the float bined floats then open the air valve 25.

does not open it immediately; the suspension continues to rise and lifts the cylindrical float from the spring 35 on which it rests, the top of this float, finally abutting against the underside of the disc 33 attached to the top of the stem 32 of the air valve operating float 30, and the com- Thus air is allowed to enter the top of the pump through an air hole 36 and the open valve 25, and this releases the vacuum. The inlet valve 27 for the suspension is held closed by the weight of the suspension, which flows through the outlet valve 28 into the constant head feed reservoir (not shown).

As the suspension in the pump falls the cylindrical float 29 descends with it but the air valve operating float 30 remains in position, keeping the air valve 25 open until the cylindrical float 29 abuts against the spring 35 on the body portion 31 of the float 30. Both the floats are then lowered until the top of the stem 32 of the air valve operating float 30 allows the air valve 25 to close, after which the vacuum once more draws the suspension into the pump and the cycle is repeated. Thus there is an intermittent supply of suspension to the constant head reservoir at a rate depending on the size of the pump used.

In this figure both the inlet and outlet valves 27, 28 for the suspension are shown as being of the stemmed, or mushroom, type having a head 37, 38 respectively arranged to fit in a valve seating 39, 40, and an upwardly projecting guiding stem 41, 42. The outlet valve 28 is arranged to be vertically above the inlet valve 27, and both the head 38 and stem 42 of the outlet valve are hollow, the stem 41 of the inlet valve being arranged to slide within the hollow stem 42 which acts as a guiding sleeve for it. The stem 42 of the outlet valve is arranged to slide within an additional guiding sleeve 43 situated above it. The air valve 25 also consists of a head 44 arranged to fit in a valve seating 45, and an upwardly projecting stem 46 arranged to slide within a guiding sleeve 47. In addition the valve includes a short stem grease? 48 projecting vertically downwards from the centre of the head 44, the top ofthestm; 32 of the air valve operating float 30 being arranged to abut against the lower end of this stem 48 for lifting and opening the valve.

Other types of valves, for example ball valves, may, however, be used if desired.

Referring now to Figure 4 the lamp envelopes 22 are arranged to be fed horizontally along on a continuously moving conveyer whilst held with their axes vertical, the conveyer (only part of which is shown) comprising two endless conveyer belts 49 arranged to revolve in synchronism, each in a substantially horizontal plane with one belt vertically above the other. The belts carry between them a plurality of vertically held battens 50, the battens being symmetrically spaced around the belts.

At the bottom of each batten is attached a stainless steel bracket 52 comprising a short upward projection 53 over which the bottom end of a tube can be placed, the tube being supported vertically by means of a spring clip 54 attached to the batten near the top end thereof. Each clip is formed of two resilient metal fingers arranged to grip the tube between them. A channel 51 of stainless steel is situated beneath the battens in the region of the coating position to collect the excess suspension draining from the tubes and lead it back to the reservoir tank 1.

It will be apparent that more than one spring clip may be attached to each batten, for supporting the tubes at several points along their length, and that other. suitable kinds of conveyer may be used if desired.

When a tube reaches the coating position, the valve nozzle assembly is lowered until the holes 13, 14 in the cylinders 9 and 10 are inside the top of the tube, the nozzle being arranged to move along with the tube for a short distance. After the lowering of the valve nozzle assembly 8 the control cylinder It) is rotated through approximately 45, allowing the suspension to flow into the tube for about 5 seconds, and is then rotated to close the nozzle holes and cut off the flow of suspension. The valve nozzle assembly is then lifted from the tube and is returned to its original position ready for coating the next tube on the conveyor. The suspension, after being introduced into the top of the tube, runs down the internal wall of the tube and coats it, the excess suspension being allowed to drain from the tube into the drip channel 5'1 and return to the reservoir tank 1.

The coated tubes finally pass to a drying chamber (not shown before being removed from the conveyor.

Referring now to Figure 5 in a particular arrangement for coating tubes held with their axes inclined both to the horizontal and to the vertical, the pump assembly 3 is similar to the one already described but the control means for the flow of suspension is combined with the constant head feed reservoir 4. The outlet pipe 61 consists of a short length of tubing 55 connected to the reservoir by a flexible stainless steel pipe 56, the outlet of the nozzle being arranged to be held just above the top of a tube 22 in the coating position and to move along for a short distance with the tube, so that the suspension on being discharged from the nozzle passes directly into the tube. The control valve means comprises a needle valve 63 in the constant head feed reservoir 4 situated at the top of the outlet tube to the nozzle and arranged to be externally operated.

The tubes 22 are arranged to be fed along on a conveyer 49 whilst held in the vertical position, the conveyer being similar to the one already described with reference to Figure 4 and the same parts are denoted by the same reference numerals; the tubes 22 are supported near the top by spring clips 54 and at the bottom by short upward projections 53 over which the tubes are arranged to be placed as already described. In operation when a tube reaches the coating position it is withdrawn from the spring clips 54 holding the upper end, and laid at an 6 angle of approximately 45 on a pair of adjacent cylindrical rubber rollers 57 with the top of the tube immediately beneath the nozzle outlet and with the bottom of the tube supported by the upward projection 53. The two rollers 57, which are arranged to move along in synchronism with the conveyer whilst carrying the tube, are arranged on the same level with their axes parallel and inclined at an angle of 45 to the horizontal, their curved surfaces being adjacent to one another but not in contact. While the tube is lying in the inclined'position a third cylindrical rubber roller 58, with its axis parallel to the axes of the other two, is brought down on to the tube, just above the other rollers 57, to hold it in position on the pair of rollers, and the tube is rotated at about 60 R. P. M., by means of one of the rollers which is driven by means of an electric motor 62. The roller 58 is shown supported between two parallel metal arms 59 which are pivoted at their other ends about a shaft 60 arrayed parallel to the axes of the pair of rollers 57, the roller 58 being arranged to be brought down on to a tube 22 lying on the rollers 57, by movement of the arms 59 as indicated by the arrow. Whilst the tube is rotated the control means for the suspension is opened to allow the suspension to flow for about 10 seconds, after which period the control means is closed, the upper roller 58 is removed from the tube, and the tube returned to vertical position on the conveyer, the excess suspension being allowed to drain from the lower end of the tube into the drip channel 51 and finally back into the reservoir tank (not shown). The nozzle and the rollers 57 and 58 are then returned to their original position ready for the coating of the next tube and after each tube is coated it is passed to a drying stage as before in order to evaporate the liquid and leave a coating of fluorescent material on the wall of the tube.

If required the same amount of suspension may be fed into the tube over a period of 5 seconds, the tube remaining on the rollers for a further 5 seconds and rotated at the same rate whilst the suspension is introduced into the next tube, a second set of rollers then being required.

cos. of suspension has been found sufficient to coat tubes having a length of 5 feet and an internal diameter of 1 /2 inches, but this amount can, of course, be varied to suit the size of the tube to be coated or the characteristics of the suspension.

It will be apparent that the conveyer, instead of being of the continuously moving type, may be indexed if desired, the tubes stopped in the coating position for the introduction of the suspension.

We claim:

A vacuum-operated pump comprising a substantially cylindrical body having at its upper end a conduit for application of vacuum and a normally closed air inlet valve including a weighted closure member and vented to the atmosphere when in open position, an inlet adjacent the lower end of said body, an inlet conduit connected to said inlet through an inlet check valve, an outlet conduit connected to said inlet through an outlet check valve, and a compound float in said body comprising a first float having a body portion with a stem portion projecting upwardly therefrom and spaced below and in alignment with the closure member of said air inlet valve and a second float in the form of a hollow-walled cylinder loosely surrounding said stem portion of the first valve and being of shorter length than said stem portion, and stop means at the top of said stem portion engageable by said second float, the buoyancy of said floats and the weight of the closure member of said air inlet valve being so proportioned that upon rising of the first float due to entrance of liquid into said body, the first float engages the said closure member of the air inlet valve but has insuflicient buoyancy to raise it to open position, the added buoyancy of the second float being suflicient to open said air inlet valve upon continued rise of the liquid with consequent lifting of said second float into engagement with said stop means.

References Cited in the file of this patent UNITED STATES PATENTS 566,625 Savorgnan Aug. 25, 1896 992,711 Freeman May 16, 1911 1,384,048 Coates July 12, 1921 2,292,862 Barton Aug. 11, 1942 

